"It's too early to talk about the detailed findings of that investigation, there's a lot of work that needs to be done," Ms Seymour said when asked about the seeming appearance of rust at the bottom of the sign.

"There's a lot of work that needs to be done with metal specialists and other specialist engineers to really look at the sign, what's happened, look at the footage, really understand the root cause."

On Wednesday one of the directors of Major Road Projects Victoria (MRPV) said the "extremely rare event" of a sign falling on a car seemed to be caused by the sign's connection with the gantry.

Inspections of others signs underway

Ms Seymour said similar-sized signs and gantries around the state were being audited, and no issues had been uncovered in the first six audits carried out so far.

"If we were at all concerned about community safety, we would close the road," she said.

"We have deemed there is no risk to community safety at this point."

However the second sign on the gantry at the centre of the incident has been taken down for an inspection as a precautionary measure.

"They have taken down one other sign on that cantilever in order just to satisfy themselves that there's nothing that would have contributed on the cantilever itself," Victoria's Acting Premier, Tim Pallas, said.

Mr Pallas called the dashcam footage a "traumatic and dramatic piece of vision".

"I hope that the person involved is well," he said.

"Certainly the damage that's been caused to the car is quite obvious and the state will pick up the appropriate damages as a consequence through our TAC [Transport Accident Commission] regime."

He assured concerned road users they should feel safe.

"Because people, with a fair degree of reason, would be concerned about signage on that section of freeway, the major road projects authority has overnight inspected all the signs and have satisfied themselves that those signs are in good order," he said.